FIG. 10(a) is a schematic drawing of a conventional micro-ball mounting device that uses a transfer mask. The micro-ball mounting device is equipped with a stage 20, on which the substrate is placed, and backup blocks 22, which are mounted on either side of the stage 20. A substrate is mounted on the stage, with its molded resin 26 facing downward so that the micro-ball mounting surface is open to the top. A transfer mask 28 is registered with the substrate 24 and its perimeter is affixed by vacuum adhesion, etc., to the backup blocks 22. In addition, a magnet is arranged inside the stage 20, so that the center of the transfer mask 28 is drawn toward the stage 20 by the magnetic force of the magnet.
When the micro-balls are dropped into place using the transfer mask 28, it is preferable that the distance (gap) between the transfer mask 28 and the mounting surface of the substrate 24 be fixed and that, in other words, the back surface of the transfer mask 28 be parallel to the mounting surface of the substrate. If the gap between the transfer mask 28 and the mounting surface of the substrate 24 is too great, or the gap is not constant, a plurality of micro-balls will drop into one of the through-holes in the transfer mask 28 and the micro-balls that have dropped in will not be positioned accurately in the terminal areas on the substrate 24.
In the case of surface-mount packages, such as BGA, molded resin is formed on the other surface of the substrate, and warping develops in the substrate due to the effects of thermal contraction, etc., of the molded resin. If the warping in the substrate is great, the aforementioned gap becomes to great or the gap becomes nonuniform. Therefore, in micro-ball mounting devices, the mounting surface of the substrate is mounted so that it extends somewhat beyond the surface of the backup blocks 22, with the edges of the substrate 24 pressed down by the perimeter of the transfer mask 28 to correct warping of the substrate. Furthermore, by attracting the center of the transfer mask 28 with a magnet, the transfer mask 28 and the mounting surface of the substrate 24 are drawn together so that the gap between them is constant.
FIG. 10(b) is a magnified drawing of area A at the perimeter of the transfer mask shown in FIG. 10(a). As shown in this figure, when the edge 24a of the substrate 243 is pressed down by the transfer mask 28, if the transfer mask has high tension or rigidity, the transfer mask 28 is substantially held up by reaction from the edge 24a of the substrate 24, and a larger-than-necessary gap d develops between the mounting surface 24b of the substrate and the back surface of the transfer mask in which the through-holes have been formed. If this gap d is outside the tolerance range, there will not be appropriate contact between the micro-balls that have dropped in and the terminal areas on the substrate 24, so that the micro-balls will drop from the terminal areas while the substrate is transported to the reflow soldering process, or the connection strength of the reflow-soldered micro-balls will be weak, or will cause pitch variations between the micro-balls, which causes defects and voids in the semiconductor device, and which in turn decreases yield and increases product cost.
The present invention resolves such problems of the prior art, and its purpose is to provide a mask, a semiconductor manufacturing device, and a semiconductor manufacturing method that uses said mask and that can appropriately drop ball-shaped metal terminals onto terminal areas on a substrate.
Another purpose of the present invention is to provide a mask, a semiconductor manufacturing device, and a semiconductor manufacturing method that uses the mask and that can improve the yield and decrease the production cost of surface-mount semiconductor devices such as BGA and CSP, etc.